Shellac

Hello! I have Ampeg SVT 410HLN cabinet and the crossover seems to have stopped working; apparently this is a common fault. The horn controller has completely stopped working and cab seems a lot less responsive. I have replaced all four 10" speakers, cleaned/checked the wiring, replaced the bulb and used my head with a similar Ampeg cabinet (to rule out the head) but it continues to sound dull and quiet. Has anyone been able to source a replacement crossover for Ampeg cabinets? Many thanks! Ben